This really depends on your comfort level and sensitivity.
The best way to whiten your teeth would be the slow and steady process. Start slowly and with short sessions. There is no rush and you have a lot of gel that will last a year.
After your first whitening session, wait for a 24 hour period and if you do not feel any sensitivity you can do another session.
We do not recommend back to back sessions for more than 3 days even if you feel comfortable. Your gums need some time to tolerate the treatment.